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primary v. secondary bond


hokeyhydro

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RE: WEST resin or like epoxy marine resins. After dozens of builds, many race boats that undergo max stress, I have never had a "secondary" epoxy joint let go, yet some folks raise a red flag over secondary bonds.

Has anyone here actually tested the strength difference between primary & secondary bonds?

Or tested the difference between a secondary bond made by coarse sanding the substrate epoxy coated base v. secondary bond made after removing peel ply?

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I have built 3 boats using secondary bonds only and never had any problems. The designers of these boats suggest it. Before cutting up any plywood, lay the sheets down flat and roller with epoxy. Once cured, sand then cut and build the boat. It is a lot easier than epoxy coating a boat once built. No runs on vertical surfaces and so on. I didn't do it on my Spindrift and now wish that I had. I start my next boat soon and will definately be switching back to precoating with epoxy before the build.

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I have built six boats and never had any issues with secondary bonds. I have always strived for chemical bonds, but if the secondary bond is clean and roughed up a bit it will hold just fine.

I will be glassing in the 2000 lb keel on our 28 one day and it will all be secondary bonds, along with keel bolts.

When you really think about the bonds we make with plywood, most are just as dependent on the glue in the laminate as the joint we are making. If that thin glue line delaminates in the plywood, it really doesn't matter to much about the prep that went into the taped joint. Of course with stitch and glue most of the time your thickened epoxy gets into the end grain of the pieces being glued up and this is beneficial in many ways.

What Jack said is definitely the easiest way to do a boat.

Just a few thoughts.

Scott

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What I figured since most of the joints on my race boats were secondary. Only problem I see with a total precoat is if the epoxy goes full cure - not green - sometimes the panels don't want to assume designed curves because they get stiff, But as ,mentioned precoating many panels is far easier than coating after they become a boat and you have to work around bulkheads, frames, and whatall.

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I recommend http://www.westsystem.com/ss/techniques-materials/ browsing through the materials West Systems Presents on the subjects, and check out the online magazine. They have done extensive tests and publish the results.

http://www.hudsonaquatic.com/aquatic-systems-for-people/therapy-pools-for-people-hydrotherapy my fathers company before he sold it, used to build these above ground pools, with laminated wood beams (beam press bases on Guergon BRO design), then coated in 3 coats of epoxy and covered with Varathan Water Varnish. Never had any problems with secondary bonding issues.

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If I was building say another Belhaven, I would do the precoat thing on all inside panels. It would save endless hours of work and I would end up with a much slicker finish on the inside. Off the top of my head I can only think of two areas that I wouldn't precoat.

The first being the top of the floor doubler where the centerboard trunk attaches. The second would be the outside of the hull that would be glassed.

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I have seen a lot of secondary bonds with epoxy fail over the years. It is impossible to build a boat without secondary bonds and if they are well prepared there is no problem. Just make sure that the joint is well sanded and clean.

While I understand Scott's statement about pre-coating the hull panels, I prefer to leave them bare so that the most important joints on the hull are primary.

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There were times when I tried to achieve both precoat and primary bond. On the underside of the rear deck I marked out where there would be contact with the inwales and deck beams. I put one or two coats on the unmarked areas then an hour or so before putting the deck on I coated the entire panel. This takes some extra time and planning but in some areas I think it was worth it. Having the best of both worlds.

If you look closely you can see the resulting pattern on the underside of the rear deck.

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I've considered that - coating all but glue line areas. And I have considered peel ply to avoid secondary bond sanding. Rolls of peel ply strip is available in 1" on up widths = 50 yard rolls for about $12. I stil can't find actual test data on primary/secondary bond strength and my amateur garage tests came out dead even = wood breaks on both situations.

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You have to be careful or you may bias your tests. From what I'm hearing, depending on the epoxy and hardener used, you may still be getting chemical or primary bonds for as long as 3 to 5 days or more after it has hardened to the point you can sand it. If so, you could lay down two or three coats wet on wet on a panel one day, wait a day or so to let it all harden, sand it all smooth and lay on a fourth and final coat before installing and all of those are primary bonds.

Or wet out the hull to get full saturation of the wood late one day, wait until the next day for it to harden, sand that smooth, then lay on the glass and wet it out, and that is still a primary, chemical bond. In fact, you could probably let the wet out / fill of a glass cloth coating run out over a few days and it would all be a primary / chemical bond.

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  • 2 weeks later...

hi.

have anybody standards or guiding about composite secondary bonding such as "better time to assembly of two pieces after curing them whit lay-up model(out-time) or roughness of surface or surface treatment?

my issue is tee connection whit epoxy adhesive

if anybody have,please send to my mail.

very very very thanks

v.azimzadeh.68@gmail.com

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